Tianjun XieGerhard R. WittreichDionisios G. Vlachos
10页
查看更多>>摘要：Plastic waste presents an environmental threat. Chemical recycling via hydrogenolysis can convert plastic waste into waxes, lubricants, and fuels. Among catalysts, Ru stands out for its superior activity and selectivity. The chemistry of light alkane hydrogenolysis can help understanding plastics deconstruction. We perform first-principles calculations, develop descriptor-based relations, and conduct microkinetic modeling and analysis on ethane and propane. Predictions are in excellent agreement with experimental data. We identify a similar cracking pattern for both hydrocarbons entailing a deeply dehydrogenated species with the removal of four hydrogen atoms: CHCH~* +~* → 2CH~* for ethane and CH3CCH~* +2~* → CH3C~* + CH~* for propane. We find that the rate-determining step is the C-C cracking for ethane and the first dehydrogenation from the terminal carbon (CH3CH2CH3~*+~* → CH3CH2CH2~*+H~*) for propane. The vinyl species CH2CH~* produced from propane cracking is responsible for whether a single or multiple cracking events occur and effectively controls the selectivity. Specifically, ethane formation in propane hydrogenolysis is suppressed at elevated temperatures due to over-cracking via multiple (two here) cracking events being preferred over hydrogenation and desorption of ethane from the catalyst. Our workflow and models provide a baseline for future studies on heavier hydrocarbons. Insights into recent experimental studies of polyethylene over Ru-based catalysts are discussed.
查看更多>>摘要：As a critical intermediate substance or a target product, CO plays a vital role in the chemical looping processes. The control of CO conversion is significant since chemical looping processes with various target products have different requirements for CO content. In the present work, the CO oxidation behaviors with different oxygen species were investigated experimentally and theoretically with Ca-substituted lanthanum ferrite (LaFeO3) as the oxygen carrier to regulate the CO conversion. The results showed that the CO2 yield increased significantly when the adsorbed oxygen species was removed, suggesting that the lattice oxygen was the active oxygen species. It was consistent with the calculation result that the energy barrier of CO oxidation with lattice oxygen was lower than that with surface adsorbed oxygen. Moreover, the CO2 yield increased with the increase of Ca concentration, indicating that Ca doping was favorable for lattice oxygen migration and further promoted CO oxidation.
查看更多>>摘要：A visible-light-driven Z-scheme photocatalytic CO2 reduction reaction (CO2RR) to produce CO was demonstrated using an aqueous particulate dispersion containing two bare semiconductors, (CuGa)_(0.3)Zn_(1.4)S2 for CO2RR and BiVO4 for water oxidation. The semiconductors were mixed with a water-soluble cobalt tris(dimethylbipyridine) complex. The CO selectivity was 98% (against H2), and the rate of CO generation was 1-2 orders of magnitude higher than those of previously-reported aqueous suspension photocatalytic systems. O2 was continuously evolved, and isotope tracer analyses confirmed that CO2 was the carbon source for CO. Experimental studies and calculations suggest that the Co complex acts dual-functionally in synergy with (CuGa)_(0.3)Zn_(1.4)S2 and BiVO4: it behaves as an efficient ionic electron mediator, and also acts as a new active CO2RR cocatalyst after a structural change by accepting photoexcited electrons from (CuGa)_(0.3)Zn_(1.4)S2. This simple method, operating in a self-optimizing manner in solution, has great potential to help achieve sustainable, highly active artificial photo-synthetic systems.
查看更多>>摘要：Poly(heptazine imide) (PHI) has emerged as a promising photocatalyst due to its ability to store long-lived photoelectrons. In this study, we report a structure-directed approach to synthesize potassium (K)-PHI from various allotropes of polymeric carbon nitride (PCN) for facilitating photoelectron transfer and improving H2 production under visible light. The K-PHI derived from the melem units exhibits high structural intactness and produces H2 more efficiently than the K-PHIs from other allotropes of PCN. The PCN-precursor optimization, to reduce the defect states and increase cyanamide functionalities of the K-PHI, serves as a vital factor in photo-electron extraction by Pt-cocatalyst for H2 production. Moreover, the melem-derived K-PHI steadily reforms cellulose into H2 (34 μmol h~(-1)) and several chemicals for 6 days. The chemicals from the cellulose-reforming comprise C6 to C1 esters, acids, aldoses, aldehydes, and alcohols. The degradation from C6 to C1 proceeds sequentially by alternating hydrolysis and photocatalytic oxidation.
查看更多>>摘要：Fe incorporated Ni-based electrocatalysts have emerged as one of the most active oxygen-evolving catalysts under alkaline conditions and deciphering the effect of iron incorporation in enhancing the activity is challenging but critical for the catalyst design. Herein, the as-prepared nanocube Ni-based catalysts underwent a reconstruction process and transformed from γ-NiOOH to β-NiOOH structure by iron incorporation under the applied bias, which was confirmed by in-situ Raman measurement. According to the methanol oxidation current response difference, the hydroxyl adsorption intensity was proposed to be regulated by iron incorporation and the rate-determining step would be the formation of ~*OOH for Fe-doped β-NiOOH, which was further supported by DFT calculation. This work reveals the effect of iron-doped on the phase structure transform and the regulation of intermediate species elaborately and offers new insight on the understanding of the activity origins for NiFe-based catalysts.
查看更多>>摘要：Replacing the kinetically sluggish anodic oxygen evolution reaction (OER) with hydrazine (N2H4) oxidation reaction (HzOR) could be the effective approach for achieving energy-saving hydrogen (H2) fuel production in a water electrolyzer system. Thus, developing the efficient HzOR electrocatalysts, combined with the cathodic H2 evolution reaction (HER) is of vital importance for the high-rate H2 fuel generation as well as for the advancement of a N2H4 fuel cell. Herein, we utilized a facile integrated process of pulsed laser irradiation and sonochemical process to synthesize AuPt alloys by the irradiation of laser to a mixture of Au/Pt solution in methanol/DI water in varied proportions. The AuPt alloy plays a key role in the chemisorption of N2H4 on its surface, forming a dative bond involving electrons of the lone pair of nitrogen in N2H4 and empty orbitals of Pt in the alloy, indicating its high intrinsic activity against HzOR. The optimal composition of Au1Pt8 electrode demonstrates outstanding characteristics of HER with an ultralow overpotential of 26 mV at 10 mA cm~(-2) in alkaline medium while requiring 502 mV to attain 10 mA cm~(-2) for HzOR in 0.5 M N2H4/1.0 M KOH electrolyte. In addition, the assembled overall N2H4 splitting electrolyzer cell using Au1Pt8 alloys as both anode and cathode requires cell voltage of only ～0.172 V at 10 mA cm~(-2) with tremendous stability over 10 h, which is much lower than the voltage of 1.773 V required for the overall water splitting electrolyzer. The present study validates the feasibility of AuPt alloys for stimulating N2H4 fuel cells in the future to achieve both electrical energy generation and high-rate H2 fuel production.
查看更多>>摘要：Two series of copper-doped mayenite catalysts (Cu_x:C_(12-x)A7) were synthesized by one-pot-assisted solution combustion at different Cu loadings (0.06 ≤ x ≤ 1) with the aim to correlate their performances in soot combustion and the nature and abundance of the different copper species present. The atmosphere composition influence, precisely of the presence of water, was also studied. It appears that Cu(II) interacted with the C12A7 matrix in three structurally different forms: isolated-Cu~(2+), clustered-Cu~(2+), and bulky CuO particles. Cu-C12A7 catalysts exhibited enhanced activity over bare-C12A7, both in terms of soot oxidation at low temperatures and CO2 selectivity. The control over the dispersion of Cu, the texture, and superoxide concentration of the Cu-C12A7 catalysts achieved by adjusting the Cu loading and calcination temperature, appeared crucial in promoting the catalytic performance. We concluded that the well-dispersed clustered Cu~(2+) is the most likely active species responsible for the improved activity both under dry and wet conditions.
查看更多>>摘要：NiFe-based electrode materials exhibit great promise for next-generation efficient oxygen evolution reaction (OER) electrocatalysts in alkaline medium, but they are difficult to be scaled up for large-area fabrication and are lack of robust research under real industrial conditions. Here we present a rapid, room-temperature suifuration strategy that transforms stainless steel meshes into highly active and stable oxygen evolution electrodes. Such method is easy to be scaled up to produce square meter-sized stainless steel electrodes (1m x 1m) with NiFeCr-containing trimetal sulfides on the surface. In a standard three-electrode cell, the sulfurated stainless steel electrode exhibits 7.2 times higher OER activity than the corresponding stainless steel, and possesses remarkable catalytic stability for over 1000 h at the current density range of 100-200 mA cm~(-2). During the OER, the Cr and S species are demonstrated to be easily detached from the electrode surface, and the in situ formed γ-(Fe,Ni)OOH is found to be the electrocatalytic active phase. Furthermore, we integrate the sulfurated stainless steel electrode into an industrial alkaline electrolyzer as the anode (400 cm~2). Our results demonstrate that the electrolyzer based on the sulfurated stainless steel electrode exhibits a better catalytic activity than the electrolyzer based on the Raney nickel electrode, a widely-adopted electrode in commercial water-alkali electrolyzers, and delivers a catalytic current of c.a. 300 mA cm~(-2) for over 120 h under the industrial catalytic conditions (30% KOH, 80 °C).
查看更多>>摘要：Single-atom Fe catalysts are a promising substitute to Pt catalysts for oxygen reduction reaction (ORR). Adjusting metal energy level through direct atomic interface regulation can effectively improve catalytic performance but still in its infancy. Herein, highly active nitrogen and sulfur dual-coordinated asymmetric Fe center anchored in carbon nanoparticles were developed. Spontaneously absorbed OH ligand is steadily anchored in asymmetric atomic interface, constructing new FeN3S-OH moiety. Theoretical calculations reveal that the incorporated S atom combined with OH ligand as energy level modifier effectively activate Fe center by electronic modulation and d-band center shift, rendering improved ORR activity of FeNSC-2Fe with E_(1/2) of 0.913 V in alkaline, 0.806 V in acidic and 0.711 V in neutral media. The FeNSC-2Fe-based device displays high power density of 306 mW cm~(-2) in Zn-air battery and 2485 mW m~(-2) in microbial fuel cell. This work provides a new perspective for the controllable synthesis and performance optimization for electrocatalysts.
Meng-Che TsaiYohannes Ayele AwokeDessalew Berihun Adam
10页
查看更多>>摘要：Here, we show a ruthenium-titanium alloy oxide (RuTiO) on a 3D web-like titania for iodide oxidation reaction (IOR) and simultaneously to boost hydrogen production by water electrolysis. The FT-EXAFS results of Ru K-edge in the RuTiO catalyst show the presence of Ru-Ti bonding in the second shell. The developed RuTiO requires an ultralow cell voltage of 1.09 V to achieve 10 mA cm~(-2) for IOR-based electrolysis, whereas the Faradaic efficiency for H2 production is almost 100 % at the cathode. The RuTiO remains stable in a 36-hours test without degradation, indicating that the electrocatalyst could be used as a robust anode in an IOR-based electrolysis for value-added H2 production. This proves that IOR-based electrolysis is more energy-saving for value-added H2 production when compared to water electrolysis. This finding paves a route to design other electrocatalysts on 3D web-like titania with improved catalytic activity and prolonged stability for IOR-based electrolysis.
NSTL